Modern integrated circuits (ICs) often include complex circuitry that operate on a variety of signals and information. To accommodate the circuit and operational complexity, an IC typically includes one or more clocks signals that facilitate and govern its operation and timing of events. Other applications, such as communications, signal processing, and the like, often use signal sources and generators in addition to clock signals. Circuit designers desire clock generation and signal source circuits that have a relatively wide tuning-range, so as to accommodate a variety of circuits, technologies (under various process, voltage, and temperature variations), and end-user applications.
One may generate clock or reference signals in a variety of ways, including ring oscillators. Typical ring oscillators, however, suffer from certain disadvantages. More specifically, they provide either a relatively wide tuning-range with a relatively high loop gain. Those factors make the ring oscillators susceptible to noise and interference. A need therefore exists for ring oscillators that have relatively wide tuning ranges, but relatively low loop-gains.